I Will be installing a subpanel in a detached garage. The subpanel will be 60 amp. The garage is about 30' from the main-panel in-house, and I will of course get an exact length before selecting the proper gauge wiring. I'll be using pvc underground for the wiring. There is already existing wiring going underground from the house to the garage, which will no longer be used. When it comes to grounding this subpanel, should I run a grounding conductor from the main panel to the new sub, or ground the sub to earth?

Reading this answer sounds like I would have to ground the subpanel to the main, primarily because in my situation this is a new install. All other variables I have control over.

If so, I would be running 4 wires from the main panel to the sub, 2 hots, 1 neutral, and 1 ground correct?

Then, at the subpanel, the ground bus bar and the neutral bus bar would not be connected, and the grounding screw removed from the ground bus bar?

Lastly, a GFCI Breaker must be used at the main, right? I believe this is true for any subpanel in a detached building, just want to be sure.

The NEC allows for both approaches, independent grounding electrodes or grounding along with feeder conductors. With independent grounding, the neutral is bonded to the grounding system, when grounding with feeder it is not. The grounding bus is always bonded to the enclosure no matter what. I've no idea about GFCI requirements, that requirement was introduced after I stopped following updates to the code.
–
bcworkzApr 23 '14 at 1:29

2

@bcworkz New work requires a grounding conductor be run with the supply (see 250.32(B)(1)).
–
Tester101♦Apr 23 '14 at 15:04

I am about to start a very similar project. 2 Pole 60amp feed to Sub Panel in detached Shed. As per my inspector, You can install GFCI Ckt Breakers in the Sub Panel, or you should use GFCI outlets at the first plug location in each ckt coming from the new Load Center. You would install a GFCI Breaker at the Main if only running a typical 20 Amp ckt, however if you install a 60Amp breaker to feed your sub panel, then the GFCI wouldn't work there to protect the lower amp ckts in the shed... Question: If both Neutral and Ground are bonded at the Main, what is the point of even running a separate
–
BigTXJimMar 9 at 18:19